A 10-Meter AM vertical
When I operate on 10-meters, I usually hang out in the SSB part of the band reserved for novice and technician operators (28.300 MHz to 28.500 MHz). I enjoy talking with newly licensed amateur radio operators and comparing notes on antennas, rigs, and portable operations. To be honest, I haven’t thought much about the other part of the band above 28.5 MHz, partly because my old Swan 100 MX only covers up to 28.5 MHz and partly because I’m usually teaching school when that part of the 10-meter band is open. However, during the winter break, I decided to “listen up” the band on my old Hallicrafters SX-62A. The experience was an eye-opener and a thoroughly enjoyable adventure. Even without a decent bandspread control, the old SX-62A captured some intriguing QSOs between 29.000 MHz and 29.200 MHz. This is the part of the band where AM lovers congregate to swap ideas, rig modifications, and antenna experiments. That swath of frequencies is quite broad, considering there are only a few places on the HF amateur bands where AM predominates.
There are a few “calling” frequencies where AM contacts can be made, including 3,885 MHz, 7.290 MHz, 14.286 MHZ, and the ten-meter frequency of 29.000 MHz. But, from what I can tell from a cursory review of these frequencies, the ten-meter portion seems to hold most of the AM activity.
As a young radio listener in the mid-50′s, I remember the excitement of listening to hams on 10-meters as they talked with people all around the world. This was the golden age of propagation, where cycle 19 helped even modest stations get DX with the barest of equipment and antennas. Our current cycle, 24, is but a shadow of the long-gone cycle 19, but there are days where 10-meters really shines. At my location on Hawaii Island, 10-meters becomes active from noon to around 5 p.m. local time.
What tweaked my curiosity about 10-meter AM was an article by Ray Soifer, W2RS, called “10 Meter AM–A Blast From The Past”. The article was published by eham.com (http://www.eham.net/articles/29348). When I finished the short piece, I decided to build a 10-meter vertical dipole that would cover the 29.000 MHz to 29.200 MHz portion of the band. My listening tests were positive. All I really needed was a rig capable of playing “AM” in that segment of 10-meters. Most new rigs, including the FlexRadio series, can produce decent signals on 10-meter AM, as do some of the older “boat anchor rigs” such as the Collins KW-1, Heathkit DX-35, the Yaesu FT-102, and some converted CB radios (such as the old Realistic Navaho transceiver). It appears that I will have to break down eventually and buy a modern rig if I plan to use the AM frequencies available on 10-meters.
With that in mind, I decided to build and test very briefly with SSB a vertical dipole covering 29.000 MHz to 29.200 MHz.
Most of the key materials I already had in the shack. I was using an earlier version of a 10-meter vertical dipole to operate in the 28.300 MHz to 28.500 MHz portion of the band. I decided to carefully take this antenna down and store it in the shack for later use. That antennas worked very well when I wasn’t teaching during the day. The mast, coax feedline, and grounding system remained intact, so I really didn’t have to do much work to get the AM antenna working.
I assembled the antenna on the ground.
I used a 33-foot (10.06 meters) MFJ telescoping fiberglass mast for the antenna support. The mast was placed over a wooden stake driven in the ground. The mast was guyed at the 16-foot (4.87 meters) level using dacron rope.
Based on the formula 234/f, I cut two #14 AWG wires to a length of 8.04 feet (2.45 meters). This would put the antenna resonant frequency very close to 29.100 MHz. Later, I rounded off the wire length to an even 8-feet (2.43 meters).
I attached the upper antenna element to the + side of a Budwig center coax connector and the lower portion of the antenna to the – side of the center connector. Each connection was soldered, coated with a layer of clear nail polish, and wrapped with several layers of vinyl electrical tape.
Each antenna element was attached to the fiberglass mast with nylon ties.
A 50-foot (15.24 meters) piece of RG-8X coaxial cable with UHF connectors was used as the feed line. Before I connected the coax to the center connector, I made a “choke balun” from the RG-8X to keep stray RF off the feed line.
The center connector was taped to the mid-point of the mast (approximately 16-feet or 4.87 meters above ground level).
I raised the fiberglass mast onto its wooden stake and tied off the dacron rope guy lines to nearby supports.
In order to avoid skewing the antenna pattern, I led the RG-8X feed line away from the center connector at a 90-degree angle to a 16-foot (4.87 meters) pvc post about 16-feet (4.87 meters) away from the main mast. The rest of the feed line was attached to an anti-static discharge unit near the shack window. This unit was connected to a 8-foot (2.43 meters) copper ground rod driven into the earth. Short lengths of RG-8X connected the antenna to the Drake tuner (MN-4), the dummy load, and finally to the Swan 100-MX.
With the help of my Drake antenna tuner, I was able to keep the SWR below 1:5 to 1. During the tests, I used a power of 25 watts for both CW and SSB. I’ll use the antenna for its intended purpose when I get a rig capable of running AM.
Once I completed the tests, I disassembled the antenna and returned the previous 10-meter vertical dipole to its former place on the mast. The 10-meter AM vertical was rolled up and stored in a plastic bin in the store-room–ready when I need it.
Ickes, Steve, WB3HUZ. Simple Antennas for Ten Meters. (http://www.amwindow.org/tech/htm/tenmant/tenmant.htm).
HF Vertical. (http://www.arrl.org/hf-vertical).
http://www.iw5edi.com/ham-radio/46/an-effective 10-20-dx-antenna-for-deed restricted lots. A reprint of an earlier article from K7ZB.
Soifer, Ray, W2Rs. 10 meter AM–A Blast From The Past. (http://www.eham.net/articles/29348.
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Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.